The practical thing was to find rooms in the city, but it was a warm season, and I had just left a country of wide lawns and friendly trees

On the surface, Nick is just stating the obvious: New York City is uninhabitably hot in the summer, and he wanted to live somewhere that would be a bit cooler, and would have some green spaces to remind him of home.

But note that Nick is also setting up West Egg as a kind of proxy for the Midwest. The Midwest is associated with honesty and sound values—-and so are the characters who live in West Egg, Nick and Gatsby. Remember Nick’s parting shout to Gatsby: “you’re worth the whole damn bunch!” The “Great” in the title is not ironic.

While Nick consistently portrays East Egg and New York City as a world of distorted values, moral corruption, and lonely anomie, West Egg is mostly associated with positive characters, and values that Fitzgerald respects. Notably, East Egg is the “fashionable” part of the island, where Tom and Daisy Buchanan live. Nick has come to New York to be at the center of the action, but immediately chooses to live in the most peripheral part, his own Midwest in the middle of the East’s biggest city.